This invention relates to a process for working-up waste materials from barium sulfide leaching or strontium sulfide leaching.
Barium sulfide leaching is a process step in the preparation of barium compounds from naturally occurring starting material, i.e. heavy spar (barite). Heavy spar contains approximately 92 to 98% by weight of barium sulfate and additional variable quantities of calcium and iron salts, as well as silicate. The ground heavy spar is mixed with finely ground carbon and is reduced to barium sulfide at elevated temperatures (approximately 1200.degree. C.). The cooled melt containing barium sulfide is extracted with hot water to form barium sulfide lye. The barium sulfide lye obtained by this barium sulfide leaching is an intermediate product in the preparation of many different organic and inorganic barium compounds. The lye is subjected to further reactions in order to form these compounds. For example, barium carbonate can be prepared in this manner by introducing carbon dioxide. Barium carbonate is used in the glass industry.
Barium sulfide leaching leaves a residue. This residue for the most part contains barium salts, and also iron and calcium salts, particularly in the form of silicates and sulfides.
The preparation of strontium compounds is comparable to the preparation of barium compounds from barium sulfate. In this case, the starting material is the naturally occurring mineral celestite, which consists essentially of strontium sulfate. The extraction of strontium compounds from this mineral is comparable to the extraction of barium compounds described above. The ground celestite is mixed with carbon, reduced to strontium sulfide at elevated temperatures, and then the cooled melt is extracted with hot water. A strontium sulfide lye is formed. This strontium sulfide lye obtained by strontium sulfide leaching is an intermediate product in the preparation of many different strontium compounds. By far the largest part of this lye is reacted further to strontium carbonate, e.g. by introducing carbon dioxide. Strontium carbonate is used on a large scale for television picture tubes.
Strontium sulfide leaching also leaves a residue.